1. Field of the Invention
This invention relates to a window sash balance or counterbalance structure and more particularly to an improved window balance assembly especially adapted for balancing windows which may fall in a range of different weights.
2. Description of the Prior Art
Balance assemblies for various window constructions have taken many varied and complex forms. This is particularly true in connection with preformed and prehung window constructions. The simplified balance assembly which utilizes springs instead of weights has been incorporated into both the prehung and conventional window construction. Such balance assemblies, however, have not been able to satisfactorily counterbalance windows which fall into a wide range of different weights. A conventional window balance may be used to balance windows through a narrow range of different weights. For example, a particular window balance of the prior art may be used to balance windows weighing from 4 through 6 pounds inclusive, a range of 3 pounds. If this range can be increased to cover a range of 6 pounds, the inventory of balances carried by a manufacturer of window assemblies can be reduced by half. Because the window balance must be the same length as the window being balanced, a manufacturer of window assemblies must have a large inventory of balances. If the inventory can be cut in half, the manufacturer will save both money and storage area.
In the past, friction has been used as an element in controlling the balancing of windows. U. S. Pat. No. 3,358,403, owned by The Celotex Corporation, discloses a window balance assembly which uses nonrotatable grooved guide members over which the free extremity of the cord extends in frictional engagement with one of the grooved guide members. While the use of a nonrotatable grooved guide member enables the balance assembly to compensate for a range of window weights, it has been found to be complex to assemble because it requires multiple parts and is thus more expensive to manufacture. In addition, the range of window weights to be balanced has been found to be comparatively narrow.
In at least one configuration of this prior art window balance, the cord is bent at 180.degree. around one of the nonrotatable grooved guide members and the amount of friction becomes too great to permit easy opening and closing of the window.